1. Technical Field of the Invention
This invention relates generally to signal processing and more particularly to controlled signal amplification.
2. Description of Related Art
FIG. 1A is a schematic block diagram of a prior art gain circuit that is used for volume control. As shown, an input signal (VIN) is received by two variable resistors with sliding taps (RGAIN and RATTENUATION). As the names imply, RATTENUATION causes the input signal to be attenuated and RGAIN causes the input signal to be amplified. The amount of attenuation and/or amplification is based on the tap point of RGAIN and RATTENUATION, which are set in accordance with a volume control signal (not shown).
FIG. 1B is a diagram of an example prior art volume range for the gain circuit of FIG. 1A. As shown, the range varies from a minimum gain to a maximum gain in steps (e.g., 32). For low volume settings (e.g., near the minimum gain area), the RATTENUATION variable resistor is adjusted. For higher volume settings, the RGAIN variable resistor is adjusted. An issue with this circuit is that to support a wide gain range, the ratio of the smallest to largest resistor within the Rgain or Rattenuation sliders gets very large.
FIG. 2 is a schematic block diagram of another prior art gain circuit that is used for volume control. As shown, an input signal (VIN) is received by a plurality of gated resistive dividers. The resistive dividers are gated in accordance with a volume control signal to provide a desired volume level. An issue with this gain circuit is that the loading on the source of the input signal varies greatly, requiring the source to have sufficient drive to drive the lowest impedance of the plurality of gated resistive dividers. In addition, for large volume ranges, resistor mismatches and loading variations make it difficult to achieve volume step accuracy and/or monotonicity in volume steps.
Therefore, a need exists for a gain control module that overcomes one or more of the issues of the prior art gain control circuits discussed above.